This is how it is with Casualties of War, Brian DePalma's tale of an atrocity in the Vietnam War. All at once it is stunning, frightening, depressing--and a mesmerizing and unforgettable piece of moviemaking. For more than two hours you are unwillingly drawn to the awful events unfolding on the screen.

It is a picture so powerful that having seen it once, you may never dare to view it again.

But the larger story about Casualties of War--which DePalma ignores--is even more disturbing. DePalma spares us the real-life ending, possibly because it would make the film much too depressing to survive as a commercial venture.

The film's story is simple. It is the straightforward account of the gang rape and murder of an eighteen-year-old Vietnamese woman by American soldiers during the Vietnam War.

Sean Penn portrays the sergeant who runs the platoon. He is the evil energy that makes the film work. Penn's Sergeant Meserve is mad, cruel, cynical and terrifying. What's worse is that he's totally believable.

At the outset of a search for enemy caves, Meserve tells his men he intends to commandeer a village woman and bring her along. They will all amuse themselves by raping her at will. When the mission is over, they will kill her, thus destroying the evidence. It's as simple and brutal as that.

Meserve's plan shocks Private Eriksson, a rookie who won't take part in the gang rape or the murder. Michael J. Fox is cast as Eriksson. Despite his own terror of Meserve, Eriksson even toys with the idea of helping the young woman escape.

Fortunately, I have never been exposed to any of Fox's previous screen work. For that reason, I find him convincing in this role.

Eriksson is, of course, unable to stand up to Meserve and the rest of the crazed group. The woman is raped repeatedly over several days and then brutally and sloppily murdered according to Meserve's plan. After the mission, Eriksson tries to report the crime to officers in his unit. They treat him as though he's crazy. They try to dissuade him. They want no part of this business.

And because he seeks to expose the crime, Eriksson himself becomes a target for murder by his former combat buddies.

Eriksson finally finds a chaplain who will listen to his story. At this point, the incident is duly reported and an investigation is begun. Four men are brought to trial. They are all given dishonorable discharges and stiff prison sentences.

That, at least, is the way DePalma ends his film. Pauline Kael is an eccentric critic. She compares Casualties of War with Grand Illusion, Shoeshine, and The Godfather.

Vincent Canby, a more mainline critic, compares it to On the Waterfront, Prince of the City, and Serpico, all tales of men who stood up to testify against wrong even thought it made them appear to be stool pigeons. If this were a fictional account of the Vietnam War, there would be no reason to discuss the ending or any other aspect.

But Casualties of War is based on a true story that was reported for New Yorker magazine by Daniel Lang on October 18, 1969.

Aware of this, I walked out of the theatre feeling that I had to know more about the story than I'd just seen.

I went to the Phoenix Public Library and read Lang's piece, which is also called Casualties of War.

It was so astonishing that I didn't take notes. I never can get the library copying machines to work properly and so several days later, I had to go back to the library stacks in the basement and read the article again.

This isn't the context in which one wants to make bad jokes about Paul Harvey but Casualties of War cries out for the rest of the story. We really need to know what happened after the four men were sentenced.

From Kael and Canby we know that movie people have wanted to make this Lang story into a film for years.

They were afraid to make it while the war was still going on because the subject matter was too controversial. There was, of course, the additional problem of filming on location while a war was in progress. Now that the war is over, this story may still be too controversial for some.

Vietnam veterans, who are now becoming an obnoxious lobby of their own, are protesting. They say Casualties of War paints too bloody a picture of the American soldier. They even accuse DePalma of trying to make soldiers look bad because DePalma himself did not serve in the war.

The killing of innocent civilians takes place in all wars. And this isn't the only Vietnam film that depicts such actions. Platoon and Apocalypse Now show the same thing happening. The scene of the burning village in Platoon is one of the most frightening ever filmed. It comes inches short of what the My Lai Massacre was all about. Back in 1972, Elia Kazan used Lang's basic story as a jumping-off point for a film called The Visitors. For it Kazan, who had directed the Academy Award-winning On the Waterfront, wrote his own screen version of what happened after the sentencings. He put up his own money and filmed on his Connecticut estate.

James Woods, in his first starring movie role, played a Vietnam vet hunted down by ex-combat companions. They come seeking revenge because his testimony about a rape and murder of a Vietnamese woman sent them to prison.

At the conclusion, they beat Woods' character nearly to death and rape his wife.

The picture wasn't successful in this country. It was, however, a smash hit in France because the French, far enough removed from their own disaster at Dien Bien Phu, were ready to concede that Vietnam was an evil swamp that tended to drown everyone who set foot in it.

But we must get back to the story of Daniel Lang. He reported the event for the New Yorker by first reading all seven volumes of the trial transcripts in the offices of the clerk of the courts at United States Army Judiciary in Falls Church, Virginia.

Later, Lang went to Minnesota to find Eriksson, who was the only witness. Eriksson is not his real name. Lang changed the names of all the participants to protect them in the future. Eriksson reportedly still lives under an assumed name, fearful of retribution from the men he sent to prison.

Four separate trials were conducted. Eriksson was the lone prosecution witness at each one.

Eriksson told the court that the woman was between the ages of eighteen and twenty and that she had a gold tooth in the front of her mouth. Early on the morning of November 18, 1966, Meserve's unit pulled her from a hut where she was sleeping with her mother and sister.

Eriksson remembered that people kept telling him that American G.I.'s were fools for "being ready to die for people who defecated in public and whose food was dirtier than anything in our garbage cans back home."

After the first day, the woman was sick and coughing. There was a discussion over whether to kill her at once or to keep her, hoping she'd get over her cold and provide more sex for the group.

Meserve, becoming irritated because of Eriksson's refusal to take part, threatened to have him "killed in action." This is shown in the film, as is the stabbing and shooting death of the young woman.

Added to the film are a scene showing Meserve saving Eriksson's life during earlier combat action and a harrowing sequence of the death of Meserve's best army buddy. These are not part of the real record and they appear only in an attempt to humanize Meserve; to make us think he was really a decent sort who merely went off his rocker after too much combat.

DePalma tilts the deck in Meserve's favor but the sergeant still comes off as a figure from your worst nightmare. Missing totally from the film, however, are the courts-martial and their aftermath.

It wasn't until weeks after the killing that Eriksson found someone who would listen to his story. The best his own lieutenant could do was caution Eriksson to be quiet and accept a transfer to another unit. This became necessary because the members of Eriksson's squad were trying to kill him.

First to listen was a chaplain from Arizona named Gary Greenacre. Lang doesn't tell us where in Arizona Greenacre lived, merely that he was a Mormon chaplain. Greenacre called in another Mormon chaplain, Captain Gerald Kirk of Ogden, Utah.

Neither name shows up in phone directories and so it's possible that Lang also devised fictitious names for them as well.

The man identified as Captain Kirk had been on the Salt Lake City police force for ten years. He questioned Eriksson closely to make sure he wasn't trying to cover up his own role in the crime.

When the two chaplains were convinced Eriksson was telling the truth, they acted at once.

Bringing Eriksson with them, they went in search of the victim's body. Though it was almost a month later, Eriksson found the dead woman. Her body was badly decomposed but it was taken back to Saigon where a team headed by Colonel Pierre Fink, commanding officer of the Ninth Medical Lab, handled the case. (Colonel Fink was one of three pathologists who had performed the autopsy on President John F. Kennedy a few years previously.)

Shortly after the medical team examined the body, arrests were made in what the army has always referred to as "the incident on Hill 192."

First there was Sergeant Meserve. Then there was Corporal Clark, who stabbed the woman. Finally, there were the brothers, Rafe and Manuel, from San Antonio, Texas. Rafe and Manuel backed up Eriksson's story. They said they had only gone along with the rape to maintain harmony within the group.

Meserve denied the killing. He said he only had been fooling when he told the men they could rape the woman and kill her. Clark pleaded innocent, too.

All four courts-martial took place in 1967 in a thirty- by thirty-foot building with a tin roof in Vietnam. Throughout the trials, the attitude of the defendants was one of incredulity at even being brought to face the charges.

Meserve was characterized by every witness, including his officers, as a genuine war hero.

His lieutenant called him the best soldier he had ever seen. "I give him a max rating as a soldier," the lieutenant testified.

Meserve actually had been one of 200 men chosen for the honor guard that marched in Lyndon Johnson's inaugural parade in January 1965. The lieutenant was asked, "Do you think a murderer should be retained in the United States Army?"

"Not until he serves his sentence," came the answer. "Then, after rehabilitation, I think there's a difference."

"Do you think a man found guilty of murder should be punished?" "Yes, but knowing Meserve as an individual, I would accept him back in the unit. Yes, sir."

Other extenuating circumstances were offered. Meserve was only twenty and had already served a year in Vietnam. He had been brought up in poverty in Buffalo, New York. He was a lapsed Catholic who had only gone through the ninth grade. He had worked in a cannery before going into the service and had managed to save $5,000.

"There's one thing that stands out about this case," Meserve's lawyer told the court. "It did not occur in the United States. Indeed, there are some who might say it did not occur in civilization."

Incredibly, Meserve was found not guilty of rape but guilty of murder. His original sentence was ten years.

Clark, who joked that he had gutted the woman three times with his bayonet, was sentenced to life for murder.

Of the two brothers, one got eight years and the other, fifteen. All the sentences were for hard labor at Fort Leavenworth, Kansas.

The dead woman's name was Mao. Several days after she was taken away, her mother convinced a South Vietnam army unit to help her search for her daughter.

The search was unfruitful but Viet Cong agents saw the mother consorting with the enemy. They killed her a few days later. Not long after that, Mao's sister also was killed by the Viet Cong.

Someone joked to Eriksson: "Between us and Charlie, we've taken care of that whole family." Eriksson's actions were deplored by all other soldiers with whom he came in contact. They thought of him as a coward or possibly a homosexual. They believed it was pointless to ruin the careers of good soldiers.

"Why throw good lives after bad?" they kept asking Eriksson. "How could you know the dead girl really wasn't a V.C. spy?"

Eriksson had originally thought he had been assigned to a squad of psychopaths. But the reactions of his fellow soldiers in Vietnam told him that most every enlisted man he met seemed to have the same mentality.

Eriksson spent the rest of his yearlong tour in Vietnam as a carpenter and a military policeman. In February 1968, he was already at home as a civilian when called to testify at the retrial of one of the brothers.

A lawyer protested that the prisoner's rights had not been read to him properly before he was arrested. Because of that, his confession was inadmissible. He was acquitted.

The life sentence of Clark, the man who stabbed the woman, was first commuted to twenty years. Then it was reduced to eight and that made him eligible for parole after half that time. Clark told the court he was interested in going to college and majoring in philosophy or literature.

The second brother went to court on the grounds that his confession was tainted. His sentence was subsequently shortened to 22 months, and it was decided he'd already served enough time to be released.

Meserve's sentence was cut from ten years to eight. He, too, was eligible for release within half that time.

Meserve already has been out of prison for almost twenty years. Who knows what caused this terrible gang murder? The New Yorker's Kael cites Paul Fussell's new book, Wartime.

Fussell wrote of World War II atrocities: "The American military learned that men will inevitably go mad in battle and that no appeal to patriotism, manliness or loyalty to the group will ultimately matter."

How did it leave Eriksson, who will have to live with what he saw for the rest of his life?

"I guess that was the big thing that happened in the war for me," he said.

And what of Daniel Lang, the author of Casualties of War? Lang was a staff writer for the New Yorker for forty years. During that time he wrote more than 100 signed pieces for it.

Lang died of leukemia in November 1980 at the age of 68. He had spent a career writing stories with unusual twists. He had been a World War II overseas correspondent for the New Yorker in Italy, France, and England.

Lang's style was to lend a sympathetic ear to people in extreme situations. For some reason they talked to him and told him fascinating offbeat stories.

He had gone to West Germany and discovered that the current generation hardly knows anything about Adolf Hitler. He had traveled to Sweden and had listened to the sad tales of men who'd deserted the army during the war. He had attended the antiwar trial of Dr. Benjamin Spock and had given a devastating account of the government's role. After Hiroshima, he had become dedicated to learning all he could about nuclear weapons.

Lang's obituary in the New Yorker read in part: "He was an inspired reporter, a lucid and enthralling writer of rare literary powers who brought deep feeling, deep thought, deep conviction to everything he touched."

Casualties of War received an extraordinary reception from critics when it was published as a 123-page book.

The London Observer called it "a classic story of the brutalizing effects of war comparable to the Red Badge of Courage and All Quiet on the Western Front."

The Christian Science Monitor compared it to Joseph Conrad's Heart of Darkness.

Writing in the Washington Post, Ward Just said: " . . . one can only marvel at the fine sense of morality, intelligence and literary skill of the man who put it together."

Lang's highest reward came perhaps in the closing words of his obituary in the New Yorker:

"He tried very hard to understand the people he wrote about and far more often than not he succeeded . . . at once a mysterious, charming, pensive, self-effacing, worried, lovable man, he will be keenly missed by this magazine."

There was only one copy of Casualties of War listed at the main library in Phoenix. I searched the shelves for it in vain.

"Sorry," an employee at the information desk told me. "It was borrowed a long time ago and never returned.